Electrochemical cells for use as power sources, particularly in conjunction with hearing aids and other medical related devices, are known which employ soluble or liquid cathodes as opposed to the more conventional solid cathode cells. In such soluble cathode cells the active cathode material is usually the electrolyte solvent or one of the co-solvents. During discharge, the solvent or co-solvents are electrochemically reduced on a current collector such as a screen having applied thereto a mixture of an inert and electrically conductive material such as carbon black, graphite, or other electrical conductor of high surface area, and, preferably, including absorbing and binding agents. The anode for these cells is preferably lithium metal, although other active metals above hydrogen in the activity scale or electromotive series including sodium, potassium, rubidium, calcium, magnesium, strontium, barium, cesium and aluminum may be used either singly or in combination.
Cathode cells based upon the utilization of lithium as the anode active metal and thionyl chloride (SOCl.sub.2) as both electrolyte solvent and active cathode and lithium tetrachloroaluminate (LiAlCl.sub.4) as the electrolyte salt have been prepared with roughly the dimension of conventional "D" and "C" size cells, using a convolutely wound structure. "C" cells were observed to realize about 156 watt-hours per pound, about 11.6 watt-hours per cubic inch and up to about 93 watts per pound at about 3 volts potential per cell for freshly prepared cells. These high potentials and capacities make this type of cell particularly useful in devices requiring infrequent replacement of cells such as in heart pacemaker devices. However, several problems exist with this cell which presently militate against its widespread practical use.
One deficiency of the cells described above, using only LiAlCl.sub.4 as the electrolyte salt, is that filled or activated cells which have been stored, particularly at elevated temperatures for extended periods of time, will exhibit an undesirable initiation period or delay time when discharge is attempted. This initiation or delay time is due to passivation of the lithium anode, that is, formation of an electrically insulating film or layer over the lithium. In cells utilizing thionyl chloride this film is postulated to be lithium chloride (LiCl) and the severity of delay is dependent upon the conditions of storage. It has been observed, for example, that storage at about 72.degree. C for about 4 days is sufficient to passivate the lithium anode to the extent that reverse polarization of the cell for several minutes may be necessary to sufficiently remove the insulating film or layer and reactivate the anode.